Hello, A yearly allocation for the LCRC cluster has been requested with the following updated information: Submitter/PI: Randall Meyer Project Name: intermetallic Division: CSE Project title: Fundamental studies of disparate metals in p/d alloys Associated funding: NSF Other Systems: NCSA 100,000 hr/yr Science: The project will use the VASP (Vienna Ab Initio Simulation Package) code to study the formation of unique phases in nanoalloys. Experimentally our group is working with Jeff Miller and Chris Marshall to synthesize alloy nanoparticles involving a d-band transition metal and a "p-electron" metal such as Ga, Ge or Sn. One interesting aspect of these alloys is that they form intermetallics as opposed to homogeneous alloys. However, it is not known how surface segregation may manifest itself in these systems. The primary aim of the proposed theoretical work is to understand the thermodynamics of nanoparticles relative to bulk phases in an effort to understand how to improve catalyst selectivity. Project description: The project has moved in two directions simultaneously over the last year. First, we have performed PDOS calculations on Pd clusters in an effort to understand how the PDOS of Pd is related to the XANES spectra and how our results compare with previous results we have obtained on Pt. We have examined both size effects as well as the effect of simple adsorbates such as CO and H2. Our calculations for Pd follow the same trends as we had previously observed with Pt. First, we find that as the particle size decreases, the intensity of the L edge decreases in response to the undercoordination which results in an increase in pure d states on the smaller clusters. In addition, we find that for CO and H2 adsorption an increase in intensity is observed as well as a shift to higher energy. In contrast, OH adsorption results in a shift to lower energy. Recently Linic and co-workers have explained this result as a unique consequence of a highly electronegative adsor bate interacting with a nearly filled d-band In this case, the antibonding orbital lies completely below the Fermi level therefore considerable . In addition we have extended our work to alloys. Experiments have been performed at the APS at both the Pd and Pt L2,3 edges for a PdPt alloy. Comparing Pd and Pt L2,3 reveals that upon alloying there are opposite shifts in the leading edges. For Pt L2,3 upon alloying there is a decrease in adsorption edge intensity, small decrease in edge position energy and a narrowing of the edge. For Pd L2,3 the adsorption edge intensity increases, a shift to higher energy and a broadening of the edge. Simulated Pt and Pd L2,3 shows a good agreement with the results obtained experimentally Pt and Pd L3 edge. Naively one could suppose that the Pd in a PdPt alloy is in expansion since the lattice constant of PdPt is large than Pd alone. This would result in a narrowing of Pd PDOS. Conversely, one could conjecture that Pt would respond as if it were in compression (and its d-band would expand). In fact this is not the case, as the Pd/Pt PDOS shows the narrowing of the d-band for Pt in the alloy and a simultaneous broadening of the Pd PDOS in the alloy. This behavior results from the fact that Pt (as discussed previously) has a larger extent than Pd. This implies that in the alloy, Pd is now “overbonded” by Pt and experiences increased hybridization due to the larger overlap with Pt than it would have had with its Pd neighbors. Similarly, Pt is now “underbonded” by Pd since the d-orbitals of Pd do not extend as far as Pt. This differences in extent are manifested by the large increase in the melting temperature of Pt with respect to Pd. Not surprisingly the PDOS is completely with consistent with the observed XANES as the decrease in the absorption edge of Pt in the alloy stems from the increase in pure d states due to the lack of hybridization in the alloy as compared to the pure metal. Of course, Pd follows the opposite trend as it experiences greater bonding in the alloy as opposed to pure metal. Second, we have examined acrolein hydrogenation as a test reaction for an examination of alloy effects and have examined the full reaction mechanism over Ag(111), Ag3In(111) and AgIn2(110) surfaces. Acrolein hydrogenation can proceed via two paths as either the aldehyde functionality (forming propanal) or the double bond (forming propenol or allyl alcohol) may be hydrogenated. Furthermore there are two intermediates along each path as the first hydrogen is added in a different location than the second location (hydroxyallyl, allyloxy, 1-formylethyl and 2-formylethyl). Previously Rosch and co-workers analyzed this reaction network over Ag(110) and looked at the effect of subsurface oxygen and found that the barriers for these reactions increased in the presence of sub-surface oxygen but that . Our work follows that of Rosch, moving to Ag(111) (the thermodynamically preferred surface of Ag) and compares Ag with AgIn alloy surfaces as AgIn alloys have been shown to exhibit supe rior selectivity for allyl alcohol. Our initial results suggest that the activity of the Ag3In (111) and AgIn2(110) surfaces will actually be lower than Ag(111) as all barriers rise. However, the presence of In does shift the selectivity as the barrier to formation of allyloxy falls from 0.93 eV to 0.21 eVon AgIn2(110). Similarly the barriers to 1-formylethyl formation also fall from 0.64 eV to 0.34 eV. However, the lack of sensitivity to the barrier for the intermediates to propanal formation imply that the selectivity will greatly increase uon alloying. It is important to recognize that the calculations also suggest that the reactivity of the alloy will be slightly less than the pure metal due to the fact that H2 is harder to activate over the alloy. Calculations will continue on two fronts. First, we will continue our analysis of XANES data of alloys. Jeff Miller’s group has expanded their experimental study of PdX alloys to include PdAu, PdZn and PdCu. We will simulate XANES and PDOS of these alloy systems to improve our understanding of how alloying effects manifest themselves in alterations to the electronic structure. We have also begun to collect a great deal of XAS data on Ag nanoparticles. We have data at the K edge as well as both the L3 and L2 edges for a variety of particle sizes (1-10 nm). We are beginning to analyze this data and to use the EELS module within CASTEP to model the data and provide interpretation of the results. Finally we would like to correlate our calculations with pair distribution function measurements of Ag catalysts taken at the APS by Pete Chupas and co-workers. Second, we will continue to examine acrolein hydrogenation over Ag surfaces but our focus will now move to Ag(221), a stepped surface, which can be used as a model of smaller nanoparticles, in an effort to explain why the selectivity seems to decrease as the particle size decreases. Furthermore, our experiments with Marshall and Miller suggest that when allyl alcohol is used as the reactant it can easily isomerize to propanal. Therefore the purpose of the alloy may also be to restrict the degree of isomerization. One of goals for the coming year is to test this hypothesis and to determine how alloying affects the isomerization reaction. Project URL: Current FY Hours Used: undetermined amount New FY Requested allocation: 450000 Q1: 100000 Q2: 100000 Q3: 100000 Q4: 150000 Justification: Thank You, The LCRC Accounts System